Not applicable.
Not applicable.
The present invention relates to electronics enclosures and in particular to pre-defined xe2x80x9cknockoutsxe2x80x9d providing openings in the enclosures for running electrical leads from the enclosures through electrical conduit.
Metal or plastic electrical junction boxes and electronics enclosures or cabinets, such as for circuit breaker panels, machine controls and motor drives, are typically mounted remotely (for example on a nearby wall) from the associated electrical components. Power lines must be run into the enclosure and electrical leads must be run from the enclosure to the associate component. Tubular conduit is used (typically required) to encase the wire running to and from the enclosure. Consequently, the enclosures often have pre-defined punched or weakened areas in one or more walls outlining a section of the wall to be removed to provide an opening for the conduit. The opening is created by knocking on or striking the wall of the enclosure within the weakened outline, usually with a hammer, to release this xe2x80x9cknockoutxe2x80x9d section from the enclosure. Because the conduit is typically tubular with a circular cross-section, the knockout and opening are usually circular. The conduit attaches to a knockout fitting, sometimes having a resilient seal, which fits into the opening and has a threaded end on which threads a nut that holds the fitting (and the conduit) to the enclosure.
To ease removal, the knockout is typically partially punched from the enclosure wall with the wall being cut all the way through along most of the circumference except for one or two small sections that remain intact. When the knockout is to be removed, it is impacted with a hammer to break away the originally intact sections.
Some enclosures are designed to be sealed according to the standards prescribed by the National Electrical Manufacturers Association (NEMA(copyright)). For example, a NEMA 4 rated enclosure is sealed sufficiently to allow it to be sprayed down with a liquid and a NEMA 12 rated enclosure is sealed against dust, dirt and dripping of non-corrosive liquids. To meet these standards, there cannot by openings in the enclosure walls as there would be if the enclosure had partially punched out knockouts, as described in the preceding paragraph. Therefore, some NEMA 4 and NEMA 12 enclosures are made without any pre-defined knockouts. To install electrical conduit to such enclosures, the installer in the field is required to use a punch or hole saw to create the conduit opening.
To lessen the burden on the installer, some enclosures are made with the full openings (without knockouts) which are plugged or capped before the conduit is installed. This technique requires additional component and assembly cost by virtue of the plugs.
Some enclosures are made with pre-defined knockouts the outlines of which are defined by a narrowed thickness of the wall. This way, the wall remains intact so that no leakage into the enclosure can occur, while weakening the walls somewhat so that the knockout can be forced out under impact. This technique can be problematic for certain applications in which the enclosure contains electronics sensitive to shock or where the electronics must be located near the knockout location in which case it could be struck directly (and damaged) when impacting the knockout.
In one aspect the present invention provides a conduit knockout made from a wall section, having a first face and an opposite second face, defining a break-away section having a first side coplanar with the first face and an opposite second side at least a portion of which is between the first and second faces so as to create a groove in the wall section opening to the second face side of the wall section defining at least a portion of a periphery of the knockout. The wall section defines an essentially continuous, unbroken surface across the break-away section and the break-away section allows separation of the knockout from the wall section with rotation of the knockout.
Preferably the wall section is part of a plastic electronics housing and the first face of the wall section is at an interior of the housing.
In one preferred form, the knockout is circular and the break-away section includes one or more (preferably two spaced apart 180 degrees) tab portions having opposite sides at the first and second faces of the wall section.
In another preferred form, the knockout includes a tool receptor adapted to receive a tool for applying torque to break the break-away section and remove the knockout from the wall section. The tool receptor is formed as a unitary part of the wall section and has four walls defining a rectangular pocket extending to a third face on the side of the second face opposite the first face. Preferably, the tool receptor is braced at one or more sides, including gussets extending from the two short walls to opposite parts of the periphery of the knockout section, preferably near the thicker, tab portions of the break-away section.
In another aspect the invention provides a method of forming a conduit knockout in an electronics enclosure. The method includes forming a wall of the electronics housing having an inner face and an outer face and molding into that wall a break-away section at least a portion of which extends from one of the inner and outer faces to an intermediate depth between the inner and outer faces without passing all the way between the inner and outer faces so as to define at least part of a periphery of a conduit knockout. Preferably, a tool receptor is also molding into the conduit knockout to receive a tool for applying torque to break the break-away section and remove the knockout from the wall.
In yet another aspect the invention provides a method of removing a conduit knockout from a wall of an electronics housing. This method includes attaching a tool to a tool receptor portion of the knockout and rotating the knockout (using the tool in the receptor) with respect to the housing generally in the same plane as the wall in which it is formed so as to separate the knockout from the wall at a break-away section at least a part of which has a narrowed thickness than the wall originally forming a continuous unbroken surface between the wall and the knockout at one side of the housing.
Thus, the present invention provides an improved apparatus and method for providing a conduit knockout in an electronics enclosure. The knockout is molded into the enclosure housing, which can be done at the same time the housing is molded, thus eliminating the need for secondary punching steps. While the knockout is pre-defined in the housing, it need not be partially cut out because the wall of the housing is thinned at some or all of the periphery of the knockout. Thus, an inner (or outer) surface of the housing can remain intact so that debris and liquid cannot enter therein. Electronic enclosures can be formed with the pre-defined knockouts according to the present invention and still meet NEMA 4 and 12 standards. Additionally, the integral tool receptor receives a standard flat blade screwdriver, pliers, wrench or other readily available tool for removing the knockout. The knockout can be removed by a simple twisting motion, with the need to impact the housing, which could damage sensitive electronics inside the enclosure. Moreover, the knockouts can be formed to any one of the standard conduit sizes and be used with conventional knockout fittings to provide a tight, splash proof connection of the conduit to the enclosure.
These and other advantages of the invention will be apparent from the detailed description and drawings.